Astronomers are puzzled by an image of a distant cluster of galaxies in which they are lined up like a string that is stretched across the Universe.

The Japanese-built Subaru telescope, positioned on an extinct volcano in Hawaii, took the extraordinary picture.

Astronomers think the cosmic alignment has something to do with the way the cluster of galaxies is being assembled.

Most galaxies in the Cosmos belong to a cluster, and in turn galaxy clusters form clusters of themselves as well.

Come together

The Subaru image is of the central portion of a rich cluster of galaxies about seven billion light-years distant.

Hundreds of galaxies are seen in a region that is much more densely populated with galaxies than our own region of space.

Astronomers are intrigued by the lining-up of the galaxies. The filamentary structure even extends outside of the image.

To them it suggests they are witnessing the cluster in the process of formation by gathering galaxy groups along the chain-like structure and growing into a larger system.

Also seen in the image are a large number of blue, arc-shaped galaxies. These are background galaxies whose light has been bent by the gravity of the nearer cluster.

By analysing those distorted images astronomers will be able to map out in detail the distribution of mass in the cluster and see what is going on to cause the galaxies to align in such a strange manner.